The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Modern motor vehicle automatic transmissions typically utilize a plurality of planetary gear assemblies disposed in tandem and a plurality of clutches and brakes that act upon elements of the planetary gear assemblies in accordance with a control scheme to provide a sequence of forward gears or speed ratios and reverse.
In certain applications, it is desirable that two planetary gear assemblies be arranged concentrically, or nearly so, in an axial plane. Such a configuration is referred to as “stacked.” A stacked planetary gear assembly provides significant gear ratio flexibility in a very compact package. Such a stacked planetary gear assembly typically requires a center or intermediate component which is a combination of the ring (outer) gear of the inner planetary gear assembly and the sun (inner) gear of the outer planetary gear assembly.
Unfortunately, difficulties attendant the manufacture of the intermediate component or combination gear have limited the availability and thus the use of stacked planetary gear assemblies. For example, the combination gear, which preferably has a thin section, typically necessitates the forming of a precision helical gear on both the inside and the outside of the component. Additionally, the component must also undergo heat treatment and the dimensional and geometry changes brought about by such heat treatment must be both minimal and minimized if the component is to meet functional requirements.